Raku pottery or Raku ware originated in Japan in the 16th century. The master potter, Chõjirõ, after firing, rapidly cooled his pots. Because of his masterful work, Chõjirõ was given a gold seal bearing the mark Raku. The family adopted the name and continued the firing process that bared their name.
Reading about "Raku-ware" in a book by reknown English potter, Bernard Leach, an American potter, Paul Soldner started exparimenting with the process of removing pots from the kiln red-hot. He found different glazes and chemicals caused different effects when placed in conbustible materials. Paul Soldner is attibuted the name the "Founder of Western (or American) Raku."
Today, Raku is defined as ceramics removed from a kiln at a high heat and combined with conbustibles to create a cause & effect with the glazed ceramic piece.

Or how the heck did he get all those calors on his pots. The process described below is specifically for copper mat glaze. There are many variations of the Raku process that will yeild different effects, colors and textures to different glazes and clays. This is how I do my pots and not a "bible" on how to do all Raku.

STEP 1: The glazed ceramic piece(s) are placed in a Raku Kiln

Raku Kiln: A specially designed kiln that opens up for quick easy access to the pots. They are usually gas-fired. Often raku kilns are hand made(like mine) as commercial ones can be pricey!

STEP 2: Heat in kiln to 1500 degrees f.

Not quite the temperature of the sun, but still pretty hot. Though in the ceramic world, it is considered low-temperature.

STEP 3: A post-fired reduction chamber (PFRC) is prepared with combustibles.

Yes, that is a metal garbage can filled with wood chips and newspaper. The lid is lined with wet newspaper.

STEP 4: Pieces are removed from kiln when the kiln reaches 1500°f.

Ouch... Hot! (Special gloves rated to 2000°, don't try this at home! Most raku-ers use tongs.)

STEP 5: Pieces are placed in the PFRC & covered causing a reduction of oxygen.

Pot(s) are put in the garbage can. The flames burn off all the air the can.

STEP 6: After 2-5 minutes the PFRC is briefly opened & a re-oxidation of the pieces is preformed.

Called "Burping the can" the lid is removed for 5-10 seconds.

The reigniting of the combustibles and the rapid cooling causes the colors to materialize.

The magic happens! (or not.) Sometimes the pots have to be refired 2, 3 or 4 times.

STEP 7: The pieces are allowed to cooled in the closed PFRC for 30-45 minutes & then inspected. They are either saved or refired.

If I like it, I wipe the ash off of them and treasure them until sold to a much appreciated art lover. If I don't like it, back to the fires! It keeps going through the cycle until either it comes out wonderful or breaks.